1. Field of the Invention
The present invention relates to a piezoelectric thin-film resonator and a process for producing the same. In particular, the present invention relates to a piezoelectric thin-film resonator including an acoustic reflecting layer acoustically separating a thin-film portion containing a piezoelectric thin film sandwiched between a pair of electrodes from a substrate, and a process for producing the same.
2. Description of the Related Art
An example of a piezoelectric thin-film resonator using a bulk acoustic wave (BAW) in a piezoelectric thin film is a piezoelectric thin-film resonator using an acoustic reflecting layer acoustically separating a thin-film portion containing a piezoelectric thin film sandwiched between a pair of electrodes from a substrate.
With respect to such a piezoelectric thin-film resonator, for example, Japanese Unexamined Patent Application Publication No. 2002-278558 proposes a structure in which a conductive acoustic reflecting layer doubles as an electrode. The conductive acoustic reflecting layer includes a first conductive sublayer and a second conductive sublayer, the first and second conductive sublayers being alternately laminated and having different acoustic impedances. The conductive acoustic reflecting layer reflects an acoustic wave traveling toward a substrate to return the reflected wave to a thin film side.
Japanese Unexamined Patent Application Publication No. 2003-258594 discloses that, with respect to a surface acoustic wave (SAW) device using a surface acoustic wave on a piezoelectric thin film, providing an epitaxial Al film having a twin-crystal structure on a piezoelectric substrate composed of a LiNbO3 or LiTaO3 single crystal enables the improvement of power durability.